Star or Delta?

[Apprentice]

I removed a 2.2kW motor which only had three electrical connections. It's operation was to drive an agitator and was DOL. Due to the gear box failing it was replaced. The new motor came and had the ability to be wired in star or delta by connecting a supplied comb which ever way you wanted for star or delta. I wired the motor up to run in delta yet the motor tripped out after 10 seconds. I changed the comb over to star and ran the motor up. All is now fine, but, how do I recognise which way to connect up in the future?

 

Thanks

[marke]

Hello Apprentice.

 

Welcome to the forum.

 

It is common for small motors to be supplied in "dual voltage" format.

This would normally bge shown on the motor name plate.

If the motor is to be used on the low voltage, connect in delta and if the motor is to be used on the high voltage, connect in star.

 

In this country, a motor of that size would be supplied for 230/400 volt operation 230V in delta and 400V in star.

Larger motors are supplied for star/delta starting and are in effect dual voltage 400/660V and so are run in delta.

To be used with a star/delta starter, the actual line voltage must equal the lower voltage rating of the motor.

i.e. a 230/400V motor could be star/delta started on a 230V 3 phase supply but not a 400V supply.

 

Best regards.

[petronila]

Mark, I am agree with your comments , but I think this information most be name plated. Usually the manufacturers show in the name pate the voltage with the triangle or star.

 

Or you could find some additional connection name plate.

 

always is better follow the nameplate indication.

 

FOR A SIX WIRES MOTOR:

 

In the case you don´t count with name plate the better way is to run the motor with no load first in Star and watch the current if is too low the good connection is Delta.

 

Regards,

Petronila

[Chris57]

Hello apprentice,

 

I'm New to this forum myself but i would just like to say keep asking questions, not just while your an apprentice but throughout your career there are a few guys out there who really know thier stuff and never be affraid to ask. ...As for the connection of your motor the six connections are really just the ends of the three sets of windings in the motor taken to a convenient point under the lid for access in the case of your first motor this was obviously designed to operate in star connection: hence three ends available and the other three linked internaly out of harms way ( a bit of a pest when it comes to testing the windings) for star Bridge

U1. V1. W1. and Then Connect L1. L2. L3 to

W2. U2. V2. you will note that I have not got the second connections in the same order This is because it makes it easier inside the cover to connect for DELTA by Bridging

U1. to W2. V1. to U2. and W1. to V2 Hope this Helps

[vidyanand]

Hello Marke,

 

Refer to a part of your message below:

 

"In this country, a motor of that size would be supplied for 230/400 volt operation 230V in delta and 400V in star.

Larger motors are supplied for star/delta starting and are in effect dual voltage 400/660V and so are run in delta.

To be used with a star/delta starter, the actual line voltage must equal the lower voltage rating of the motor.

i.e. a 230/400V motor could be star/delta started on a 230V 3 phase supply but not a 400V supply."

 

The place i work has phase to neutral voltage of 230v and phase to phase voltage of 400v. As per the above message, any motor i need to use here in star/delta configuration has to have a rated voltage of 400/660v. Let me know if i getting it right.

 

I have some AC drives with 3 phase output of 200/240v. Can this be used for 400/660v ac motor?

 

Please explain.

 

Regards,

 

Vidyanand

[mariomaggi]

Dear vidyanand,

you don't write on your profile where are you living, therefore I cannot know your local frequency.

 

I have some AC drives with 3 phase output of 200/240v. Can this be used for 400/660v ac motor?

Yes, but only at reduced power, with normal torque.

 

If your drives could output 240 V as maximum voltage, the maximum working frequency will be:

Motor nominal frequency / 400 x 240.

Therefore for 60 Hz:

60 Hz / 400 V x 240 V = 36 Hz.

 

Motor must be connected in this case in delta; from low frequency to 36 Hz you will have the nominal torque, over 36 Hz the torque will decrease quickly, therefore only few applications could be powered.

 

Please note that there are no 400/660 V motors, the values are always in the ratio 1:1.73

 

Regards

Mario

 

[vidyanand]

Hello Mariomaggi,

 

Thanks for your explaination.

 

I am from Tanzania. The frequency here is 50 Hz.

 

If your drives could output 240 V as maximum voltage, the maximum working frequency will be:

Motor nominal frequency / 400 x 240.

Therefore for 60 Hz:

60 Hz / 400 V x 240 V = 36 Hz.

 

Maximum working frequency = Frequency/400 V x 240 V

 

Is 400 V in the above formula the nominal working voltage of the motor?

 

Thanks,

 

vidyanand

 

 

[santuusa]

hello friends,

I am newly pass out electrical engineer.

I am facing problem in star/delta starter.

my question is up what rating of motor the dol stater use and why?

Also upto what rating of motor the star-delta starter use and why?

 

Please expalin.

 

 

 

 

 

Hello Marke,

 

Refer to a part of your message below:

 

"In this country, a motor of that size would be supplied for 230/400 volt operation 230V in delta and 400V in star.

Larger motors are supplied for star/delta starting and are in effect dual voltage 400/660V and so are run in delta.

To be used with a star/delta starter, the actual line voltage must equal the lower voltage rating of the motor.

i.e. a 230/400V motor could be star/delta started on a 230V 3 phase supply but not a 400V supply."

 

The place i work has phase to neutral voltage of 230v and phase to phase voltage of 400v. As per the above message, any motor i need to use here in star/delta configuration has to have a rated voltage of 400/660v. Let me know if i getting it right.

 

I have some AC drives with 3 phase output of 200/240v. Can this be used for 400/660v ac motor?

 

Please explain.

 

Regards,

 

Vidyanand

 

[marke]

Hello santuusa

 

Welcome to the forum

 

The use of DOL starters and star delta starters is very dependent on the local conditions and regulations or codes.

In much of the 50Hz supply world, it has been the norm to have a local requirement for the use of a reduced voltage starter for all motors greater than 4KW.

The star delta starter has been the traditional solution to the reduced voltage starter requirement, but in reality, in many installations, causes more damage and interference than DOL.

Today, the requirements in some areas have changed. We had some regions here in New Zealand that insisted that star delta starters were used on all motors from around 4KW to around 55KW, and that autotransformer starters were used above that figure.

Today, the suply authorities are more relaxed and in some cases will specify the maximum start current and leave it up to the installer to determine the best starter.

 

Personally, I will never use a star delta starter as in the majority of cases, there is not sufficient torque in star to get the motor to full speed and therefore you are better going DOL.

My choice is for the use of a soft starter as you can contol the start characteristics to more closely match the load characteristics.

 

Best regards,